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CVE-2026-78209— exceljs through 4.4.0 CSV Formula Injection via Unescaped Cell Values

Quick assessment

Affected
exceljs exceljs
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

exceljs是exceljs组织的一款读取和写入Excel文件的JavaScript库。 exceljs 5.0.0之前版本存在输入验证错误漏洞，该漏洞源于未能中和写入CSV输出的单元格值中的前导等号、加号、减号或at符号，可能导致攻击者注入公式，当CSV文件在电子表格应用程序中打开时执行，从而泄露数据或进行其他恶意操作。

CVSS 8.2 · High EPSS 0.41% · P34

Affected Version Matrix 1

VendorProduct Version RangeStatus
exceljs exceljs ≤ 4.4.0 affected
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I. Basic Information for CVE-2026-78209

Vulnerability Information
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Vulnerability Title
exceljs through 4.4.0 CSV Formula Injection via Unescaped Cell Values
Source: CVE Program / CVE List V5
Vulnerability Description
exceljs through 4.4.0 fails to neutralize leading equals, plus, minus, or at signs in cell values written to CSV output. Attackers who can influence exported cell values can inject formulas that execute when the CSV file is opened in a spreadsheet application, potentially exfiltrating data or performing other malicious actions.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1236
Source: CVE Program / CVE List V5
Vulnerability Title
exceljs 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
exceljs是exceljs组织的一款读取和写入Excel文件的JavaScript库。 exceljs 5.0.0之前版本存在输入验证错误漏洞，该漏洞源于未能中和写入CSV输出的单元格值中的前导等号、加号、减号或at符号，可能导致攻击者注入公式，当CSV文件在电子表格应用程序中打开时执行，从而泄露数据或进行其他恶意操作。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
exceljs exceljs 0 ~ 4.4.0 -

II. Public POCs for CVE-2026-78209

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Success marker: VULNERABLE: unescaped formula in exported CSV: user_input,"=cmd|'/bin/sh -c ""echo PROOF_f6fba9086be3b9a3 > /tmp/pwned"""
Reproduction recording is a Pro+ exclusive
Watch the full sandbox build + live exploit recording for this CVE. Limited-time ¥499/mo.
Upgrade to Pro+
claude_code · 49721 chars
GitHub 复现环境（可 clone 直接跑）
Pro+ exclusive includes:
Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
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III. Intelligence Information for CVE-2026-78209

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Vendor Advisories for CVE-2026-78209 (2)

Vendor Pages for CVE-2026-78209 (1)

Same Patch Batch · exceljs · 2026-08-24 · 4 CVEs total

CVE-2026-78207 9.4 CRITICAL exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
CVE-2026-78206 7.5 HIGH exceljs through 4.4.0 Uncontrolled Resource Consumption via Unbounded xlsx Decompression
CVE-2026-78208 7.5 HIGH exceljs through 4.4.0 Path Traversal via Unvalidated addImage filename

IV. Related Vulnerabilities

Same product: exceljs
Same vendor: exceljs
Same weakness: CWE-1236

V. Comments for CVE-2026-78209

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